Yup, there is some truth in there.
Have had elk right close to camp several times now after a late night bugle or cow calling.
If you are up getting ready for the morning hunt, and you are up a couple hours before first light to prepare for your day, always worth giving a few calls!
Issue is trying to make sure the rest of your party stays quiet from that point on when moving about.
Also, after hiking into an area where you want to start your hunt from, give a few chirps, and they stay really quiet for 15 minutes.
There were times we put the bikes on the tree to get our gear out and backpacks on, but stayed quiet etc.
Would look up, not even 3 or 4 minutes and there a bull looking right at us.
Happened more than you think.
Right at first light!